1. Field of the invention
The invention relates to an axial movement gauging head for checking linear dimensions of mechanical parts, comprising a casing having substantially an elongated shape which defines the measurement axis, a shaft partially housed within the casing for performing a translational, axial displacement with respect to the casing, a feeler coupled to an end of the shaft for touching the part, transducer means for providing a signal depending on the amount of the displacement, and limiting means for limiting the displacement.
2. Description of the Prior Art
In most of the applications of the axial movement gauging heads, the heads are fixed to a stationary support, while the parts to be checked are displaced, manually or automatically, to the measurement position, on supports the position of which, with respect to the head position, does not change during the measurement and loading operations. Therefore, in practice each part reaches the measurement position due to the particular shapes of the feeler surface. The part, coming into contact with this surface, thrusts the feeler causing the translation, with respect to the casing, of the head movable armset, to which the feeler is fixed. The displacement, the amount of which depends on the part dimension, is transformed by a transducer into an electric signal which is transmitted to an electric power-supply and indication unit. In case it is desired to check parts having different nominal dimensions, in particular by using gauging heads having broad measurement range, this type of operation may suffer from drawbacks.
In fact, since the position of the part support is, as mentioned before, stationary with respect to the head, the part dimensions to be checked can be too short, so that no contact between the part and the feeler takes place, or too long, so that an undesired contact occurs between the part and a portion of the feeler different from the properly shaped surface. In the first case, obviously no checking is performed; in the second case there is a considerable risk of damaging the head.
In order to avoid these drawbacks without any need of retracting and releasing (through "retraction" devices) the feeler for the insertion of the part at any checking, it is necessary, when the nominal dimensions of the parts change, to modify the rest position of the feeler, and thus of the head movable armset, with respect to the part support. The devices used for this purpose are usually called devices for "pre-stroke adjustment".
A gauging head is known in which the rest position of the feeler is defined by the contact between internal surfaces of the movable armset and stop elements coupled to the casing. The stop elements are generally constituted by pins or dowels, arranged through suitable holes of the casing, and having a position adjustable from the outside. This type of solution requires considerable manufacturing costs of the moving armset, in particular for the internal surfaces involved. Moreover the use of tools is necessary for carrying out the adjustment. Furthermore the considerable additional cost of the device for the pre-stroke adjustment is not justified if, for particular applications, this device is unnecessary.
Generally, the design and construction of the known axial movement gauging heads considerably depend on the possible presence of devices for pre-stroke adjustment.